Rough, Unstable, or Incorrect Idle, Stalling

DEFINITION
Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall engine.

PRELIMINARY CHECKS
^ Perform the careful visual / physical checks as described in Diagnosis By Symptom/Preliminary Checks. Testing and Inspection

^ Check for vacuum leaks.
^ Check Powertrain Control Module (PCM) grounds for being clean, tight and proper routing.

FUEL SYSTEM
Check:
^ Injector balance. Refer to Chart C-2A Injector Coil/Balance Test Procedure. Chart C-2A Injector Coil Balance Test Procedure

^ For fuel in pressure regulator hose. If fuel is present, replace regulator assembly.
^ Evaporative Emission Control (EVAP) system, use Chart C-3 Evaporative Canister Purge Valve Check. Chart C-3 EVAP Canister Purge Valve Check

^ The heated oxygen sensor should respond quickly to different throttle positions. If it does not, check the heated oxygen sensor for silicon contamination from fuel or use of improper RTV sealant. The sensor will have a white, powdery coating, and will indicate a high but false signal voltage (rich exhaust indication). The PCM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.

NOTICE:
Monitoring Long Term (L.T.) fuel trim and Short Term (S.T.) fuel trim will help identify the cause of some problems. Refer to Typical Tech 1 Data Definitions for an explanation of L.T. fuel trim and ST. fuel trim.

ADDITIONAL CHECKS
Check:
^ Throttle linkage for sticking or binding.
^ Exhaust Gas Recirculation (EGR) system, use Chart C-7 Exhaust Gas Recirculation (EGR) Flow Check. Chart C-7 Exhaust Gas Recirculation (EGR) Flow Check

^ Idle Air Control (IAC) operation, use Chart C-2B Idle Air Control (IAC) Valve Check. Chart C-2B Idle Air Control (IAC) System Check

^ A/C signal to PCM, scan tool should indicate A/C is being requested whenever A/C is selected. If problem exists with A/C "ON," check A/C system operation Chart C-10A A/C Clutch Circuit Diagnosis. Chart C-10A A/C Clutch Circuit Diagnosis (C61 & C67 A/C)

^ Crankcase ventilation valve for proper operation. Refer to Positive Crankcase Ventilation.
^ Service Bulletins for Programable Read Only Memory (PROM) updates.
^ For broken motor mounts.
^ Generator output voltage. Repair if less than 9 or more than 17.3 volts.
^ Boost control system components and connections. Use Chart C-18 Boost Control Solenoid Functional Check.
(VIN 1 only).Chart C-18 Boost Control Solenoid Functional Check

^ Cruise control cable for binding or adjustment.